In the so-called information-oriented age as we are today, various types of electric and electronic information such as sound, picture, text data, binary data, etc. are now handled using diverse types of transmitting means. Of these different types of electric and electronic information, low quality voice, low speed monochrome still picture, low speed text data and low speed binary data are transmitted via public telephone line as an electric signal, high speed monochrome still picture, high speed text data and high speed binary data are transmitted by ISDN (Integrated Service Digital Network) line as an electric signal, and high quality voice and moving picture are transmitted via terrestrial wave broadcasting, satellite broadcasting or CATV as modulated wave or via optical fiber transmission route as modulated light.
In the information-oriented age as described above, attention is now focused on interactive information systems as a promising major information system, in which general public who, hitherto, have been merely receivers of the one-way information sent to them can selectively receive and positively utilize the information.
Interactive information systems currently used are answering systems using an automatic voice response system via a public telephone line, videotex systems represented by CAPTAIN (Character and. Pattern Telephone Access Information Network) using a still picture, and VRS (Video Response System) using the moving picture via dedicated line.
Among these interactive information systems, the answering system relies only on audio information. Thus, it is not possible to obtain sufficient information, and the inputted or outputted data cannot be visually confirmed.
In the videotex system, characters and pictures are displayed by using character codes. This means that there is a limitation in the contents of display, and the picture information using character codes can provide smaller amount of information than a natural picture.
The VRS system can handle natural moving picture and has no limitation in the contents of display, while communication cost is high because it utilizes a wide band dedicated transmission path.
On the other hand, in the currently available television system, information services such as television shopping, various types of subscription, weather forecast, traffic information, etc. are offered although these are not interactive. Many of these types of picture information needed in these information services are still picture information, and moving picture information is needed less frequently. In this respect, in the currently used television system offering these information services, the still picture is broadcast as moving picture. That is, by sending several hundreds to several thousands of the same picture, a still picture is displayed on the screen of a television set.
Therefore, the transmission of still picture is very costly, and it is not available to provide an interactive information service to transmit still pictures to meet the requirements of users.
For example, in case of television shopping, which is a typical information service using picture, it has been practiced to date that the user utilizes products information on the still pictures, which are sent one-way from a broadcasting station, and there have been provided no interactive information service, in which the picture of desired products is displayed on the television set according to the intention of the users and the users carry out shopping based on the displayed contents.
A television picture consists of frames. In NTSC system as adopted in Japan, the picture is sent at a rate of 30 frames per second. If one still picture is transmitted for each frame, 30 natural still pictures are transmitted per second.
As the still picture broadcasting system based on this principle, there is a system called "time-division still picture broadcast system".
FIG. 1 is a schematical drawing to explain the time-division still picture broadcast system.
In the time-division still picture broadcast system, still pictures 3-1, 3-2, 3-3, 3-4, . . . are at first photographed by independent television cameras 4-1, 4-2, 4-3, 4-4, . . . at a still picture broadcasting station 1. Then, these still pictures are composed to television signals, which comprise frames 5-1, 5-2, 5-3, 5-4, . . . and these are transmitted to still picture receiving devices 2-1, 2-2, 2-3, 2-4, . . . .
Upon receipt of the television signals, the necessary frames are stored to frame memories at the still picture receiving device 6-1, 6-2, 6-3, 6-4, . . . . Then, the stored frames are repeatedly read out from the frame memories, and are displayed as still pictures on display units 7-1, 7-2, 7-3, 7-4, . . . .
Selection of necessary frames and recording of the frames to the frame memories are performed by means such as inserting a frame identification signal to the horizontal scanning line during the vertical retrace interval of each frame.
In the interactive still picture information service system, selection of the necessary frames and recording them to the frame memories are carried out by inserting the frame identification signal to the horizontal scanning line during the vertical retrace interval of each frame at the still picture broadcasting station and by detecting the frame identification signal at the still picture receiving device.
FIG. 2 represents a method to receive still pictures using the frame identification signal. In this figure, among the elements to constitute a frame, a picture displayed on a screen is represented by reference numeral 10, and a picture identification signal inserted to the horizontal scanning line during the vertical retrace interval not displayed on the screen is represented by reference numeral 11. These are arranged in vertical direction along time base.
The picture 10 includes a menu picture 12 and information pictures 14, 16, . . . .
The frame identification signal 11 includes a menu screen identification signal 13 and information screen identification signals 15, 17, . . . . These identification signals are designed as different signals, and the desired frame can be selected according to the identification signal. In this case, the menu screen to display information of the entire still picture broadcast is used, but this menu screen is not necessarily required.
Among the frame identification signals used in the time-division still picture broadcast system, the signal inserted in the horizontal scanning line during the vertical retrace interval between frames is most generally used. In the method to use these frame identification signals, the identification signal is used for each frame. This means that it requires troublesome procedure to insert the identification signals and consumption of the radiowave resources increases because the inserted frame identification signals occupy the television signal. The present inventor has proposed a method in Japanese Patent Application 6-289357, in which a specific picture frame is set as a reference frame, and ordinary picture frames other than the reference frame can be selected by counting the number of frames based on positional relationship with the reference frame. Also, the present inventor has proposed a method to use audio band of television signal as the frame identification signal, and a method to use a frame identification signal transmitted by means other than television signal, e.g. a telephone line.
The present invention is an invention relating to the Japanese Patent Application 6-289357.